It has been proposed that the epithelium lining the bronchial airways produces bronchodilators that act to reduce the construction of bronchial smoothe muscle when stimulated. Bronchial hyperreactivity, as found in asthma, may be related to the loss of the epithelial cell lining. The epithelial derived relaxant factor may be chemically related to the relaxant factor released by endothelial cells (EDRF) lining the blood vessels, however, multiple factors may be produced by the epithelium that produce bronchodilation. Cyclic GMP is an intracellular second messenger that is known to mediate vascular relaxation to nitrovasodilators and to EDRF which is thought to be nitric oxide. Additionally, reactive oxygen metabolites have been shown to regulate guanylate cyclase, the enzyme responsible for cGMP production. Superoxide anion and hydrogen peroxide are produced and released by inflammatory cells found within the bronchial wall. Since these oxygen species may also cause cell damage and death, the effects of oxygen radicals on the bronchial epithelium, smooth muscle reactivity and modulation of soluble guanylate cyclase activity will be examined in this proposal. These studies will be done using isolated bovine bronchial tissue for studies on airway reactivity in the presence and absence of the epithelial cell lining. Biochemical studies will also be performed using the intact tissue to determine the effects of oxygen metabolites and the epithelium on intracellular second messengers that may regulate reactivity. Cultured epithelial cells will be studied for release of potential mediators of airway contraction or relaxation and or the direct effect of oxygen radicals of cell viability.